JP7273497B2 - Separator for solid electrolytic capacitor or hybrid electrolytic capacitor and solid electrolytic capacitor or hybrid electrolytic capacitor using the same - Google Patents

Description

The present invention provides a separator for solid electrolytic capacitors or hybrid electrolytic capacitors (hereinafter, "separators for solid electrolytic capacitors or hybrid electrolytic capacitors" may be abbreviated as "separators") and solid electrolytic capacitors or hybrid electrolytic capacitors (hereinafter, " "Solid electrolytic capacitor or hybrid electrolytic capacitor" may be abbreviated as "capacitor").

A "solid electrolytic capacitor" is an aluminum electrolytic capacitor using a conductive polymer as a cathode material. The conduction mechanism of an aluminum electrolytic capacitor using only an electrolytic solution as a cathode material is ionic conduction, but the conduction mechanism of a solid electrolytic capacitor is electronic conduction and has high conductivity up to high frequencies. Therefore, by using a solid electrolytic capacitor in a step-down circuit for supplying power to a CPU, for example, it is possible to obtain merits such as reduction in ripple and reduction in the number of capacitors. The use of solid electrolytic capacitors is expanding in order to meet the recent demands for smaller size and higher performance of electronic equipment.

A drawback of solid electrolytic capacitors is that they have no self-healing action when the aluminum oxide layer on the surface of the anode is damaged for some reason. In order to improve this point, a "hybrid electrolytic capacitor" using both a conductive polymer and an electrolytic solution as a cathode material has been proposed (see, for example, Patent Document 1).

As a method for holding the conductive polymer in the capacitor element, there is a method in which a monomer, which is a precursor of the conductive polymer, is oxidatively polymerized by an oxidizing agent in the capacitor element, and a method in which the conductive polymer obtained by polymerizing the monomer in advance is added to the capacitor. There is also a method of impregnating the element.

When the conductive polymer is oxidatively polymerized in the capacitor element, the capacitor element is impregnated with a solution containing a monomer and an oxidizing agent (hereinafter sometimes abbreviated as "polymerization liquid"), then heated and dried to perform oxidative polymerization. and a conductive polymer is formed in the capacitor element.

When impregnating a pre-polymerized conductive polymer, the capacitor element is impregnated with a suspension of the conductive polymer dispersed in a medium such as water (hereinafter sometimes abbreviated as "dispersion"), and then heated.・Dry to form a conductive polymer film in the capacitor element.

Heat resistance and chemical resistance of the fibers constituting the separator are important in any of the above-described methods for holding the conductive polymer in the capacitor element. Conventionally, separators for solid electrolytic capacitors with excellent heat resistance and low ESR consist of wet-laid nonwoven fabrics containing fibrillated heat-resistant fibers having a melting point or thermal decomposition temperature of 250° C. or higher, fibrillated cellulose, and core-sheath type composite fibers. , a separator for a solid electrolytic capacitor is disclosed (see, for example, Patent Document 2).

The separator of Patent Document 2 is a core-sheath type composite in which polyethylene terephthalate having a melting point of 255° C. is used as the core component and polyester copolymer (polyethylene terephthalate-polyethylene isophthalate copolymer) having a melting point of 110° C. is used as the sheath component. fiber is used. This core-sheath type conjugate fiber is used as a binder fiber, and has sufficient electrolyte resistance in the environment where conventional capacitors are used, and can be used without problems. However, when capacitors are used in automobiles, particularly when incorporated into equipment placed near the drive train of automobiles, there is a demand for capacitors that can withstand higher temperatures than ever before.

When capacitors, especially hybrid electrolytic capacitors that use an electrolyte, are used at higher temperatures than before, the fibers may deteriorate due to the action of the electrolyte solvent, etc., affecting life characteristics and reliability. Concerned.

JP-A-11-186110 Japanese Patent No. 4163523

An object of the present invention is to provide a separator for a solid electrolytic capacitor or a hybrid electrolytic capacitor that is excellent in electrolyte resistance, low resistance and highly reliable, and which can be used.

As a result of intensive research to solve the above problems, the following invention was found.

(1) A core-sheath type composite comprising a fibrillated heat-resistant fiber, a fibrillated cellulose, and a binder fiber, wherein the binder fiber has a resin having a melting point of 160°C or higher as a core component and a wet heat adhesive resin as a sheath component. A separator for a solid electrolytic capacitor or a hybrid electrolytic capacitor, comprising fibers, wherein the wet heat adhesive resin is at least one selected from the group consisting of vinyl alcohol resins and ethylene-vinyl alcohol resins.
( 2 ) The separator for a solid electrolytic capacitor or hybrid electrolytic capacitor according to (1 ) , wherein the content of the core-sheath type composite fiber is 10 to 50% by mass with respect to the total fibers contained in the separator.
( 3 ) A solid electrolytic capacitor or hybrid electrolytic capacitor using the separator for a solid electrolytic capacitor or hybrid electrolytic capacitor according to (1) or (2) above.

The separator for solid electrolytic capacitors or hybrid electrolytic capacitors of the present invention contains fine fibrillated heat-resistant fibers with high heat resistance, thereby improving the thermal dimensional stability of the separator and making it a separator excellent in heat resistance. can be done. In addition, a dense network structure is formed by the fibrillated heat-resistant fibers and the fibrillated cellulose, the formation of the conductive polymer film becomes uniform, and a separator excellent in retention of the electrolytic solution can be easily obtained. In addition, as the binder fiber, by containing a core-sheath type composite fiber having a resin having a melting point of 160 ° C. or higher as a core component and a wet heat adhesive resin having excellent chemical resistance and hydrophilicity as a sheath component, thermal dimensional stability is improved. It is possible to obtain a separator that is less likely to be deteriorated by the electrolytic solution without impairing the

The separator for a solid electrolytic capacitor or a hybrid electrolytic capacitor of the present invention contains fibrillated heat-resistant fibers, fibrillated cellulose, and binder fibers, and as the binder fibers, a resin having a melting point of 160 ° C. or higher is used as a core component, and wet heat adhesion is performed. It is characterized by including a core-sheath type composite fiber having a flexible resin as a sheath component.

A solid electrolytic capacitor is an aluminum electrolytic capacitor using a conductive polymer as a cathode material. A hybrid electrolytic capacitor is an aluminum electrolytic capacitor that uses both a conductive polymer and an electrolytic solution as cathode materials, and is also called a conductive polymer hybrid aluminum electrolytic capacitor. Conductive polymers used in solid electrolytic capacitors or hybrid electrolytic capacitors include polypyrrole, polythiophene, polyaniline, polyacetylene, and derivatives thereof.

As the electrolytic solution used for the hybrid electrolytic capacitor, an electrolytic solution containing a non-aqueous solvent and an organic salt is preferable. γ-butyrolactone, sulfolane, or mixtures thereof can be used as non-aqueous solvents. As the organic salt, an organic amine salt such as triethylamine borodisalicylate or a cyclic amidine salt can be used. The concentration of the organic salt in the non-aqueous solvent is not particularly limited, and can be, for example, 5-50% by mass.

In the present invention, the fibrillated heat-resistant fiber has a melting point or thermal decomposition temperature of 250° C. or higher, and includes, for example, wholly aromatic polyamide, wholly aromatic polyester, polyimide, polyamideimide, polyetheretherketone, polyphenylene sulfide, poly Fibrillated fibers made of heat-resistant resins such as benzimidazole, poly-p-phenylenebenzobisthiazole, poly-p-phenylenebenzobisoxazole, and polytetrafluoroethylene are used. Among these, wholly aromatic polyamides are preferable, and para-type wholly aromatic polyamides are particularly preferable, since they are easily fibrillated and have high affinity with electrolytes and conductive polymers.

In the present invention, fibrillated heat-resistant fibers refer to fibers having very finely divided portions mainly in the direction parallel to the fiber axis, at least a portion of which has a fiber diameter of 1 μm or less. is preferably distributed in the range of length to width aspect ratio of 20/1 to 100000/1. Therefore, not only the number of fibers is very large, but also the aspect ratio is very large, so that the fibrils are entangled with each other and with other fibers at a high frequency, and a dense nonwoven fabric with small pores can be formed. Therefore, a separator having excellent heat resistance can be obtained.

The modified freeness of the fibrillated heat-resistant fiber in the present invention is preferably 0 to 700 ml, more preferably 0 to 600 ml, still more preferably 0 to less than 450 ml. If the modified freeness exceeds 700 ml, the fibrillation is not so advanced and there are many thick trunk fibers, so the pore size tends to increase, and the distribution of the conductive polymer may become uneven. Electrolyte retention may deteriorate. On the other hand, when the modified freeness is less than 0 ml, the average fiber length tends to be short, and the fibrillated heat-resistant fibers may fall off from the separator. As the fibrillation of the fibrillated heat-resistant fiber progresses, the modified freeness continues to decrease. Even after the modified freeness reaches 0 ml, if the fibers are further fibrillated, the fibers will pass through the mesh and the modified freeness will start to rise. In the present invention, such a state in which the modified freeness is reversed is called "the modified freeness is less than 0 ml".

In the present invention, the modified freeness is JIS P8121-2: 2012 except that an 80-mesh wire mesh with a wire diameter of 0.14 mm and an opening of 0.18 mm is used as the sieve plate, and the sample concentration is set to 0.1%. It is a value measured according to

The fibrillated heat-resistant fiber preferably has a mass-weighted average fiber length of 0.10 to 2.00 mm. Also, the length-weighted average fiber length is preferably 0.05 to 1.50 mm or less. If the average fiber length is shorter than the preferred range, the fibrillated heat-resistant fibers may fall off from the separator. If the average fiber length is longer than the preferable range, poor dispersion is likely to occur, uneven basis weight may occur, the distribution of the conductive polymer may become uneven, and the retention of the electrolyte may deteriorate.

In the present invention, the mass-weighted average fiber length and the length-weighted average fiber length of the fibrillated heat-resistant fibers are measured in projected fiber length (Proj) mode using Kajaani FiberLab V3.5 (manufactured by Metso Automation). average fiber length (L(w)) and length-weighted average fiber length (L(l)).

The average fiber width of the fibrillated heat-resistant fibers is preferably 0.5-35 μm, more preferably 1-30 μm, and even more preferably 4-28 μm. When the average fiber width exceeds 35 μm, the distribution of the conductive polymer may become non-uniform and the retention of the electrolyte may deteriorate. If the average fiber width is less than 0.5 μm, the fibers may fall off from the separator, and the retention of the electrolyte may deteriorate.

In the present invention, the average fiber width of fibrillated heat-resistant fibers is the fiber width measured using Kajaani FiberLab V3.5 (manufactured by Metso Automation).

The fibrillated heat-resistant fiber is processed by a refiner, a beater, a mill, a grinder, a rotary homogenizer that applies a shearing force with a high-speed rotating blade, and a cylinder with a high-speed rotating inner blade and a fixed outer blade. A double-cylinder high-speed homogenizer that generates a shear force between them, an ultrasonic crusher that makes it finer by impact with ultrasonic waves, and a pressure difference of at least 20 MPa to the fiber suspension to pass it through a small diameter orifice to make it high speed. , can be obtained by colliding and rapidly decelerating the fibers, and treating the fibers with a high-pressure homogenizer or the like that applies a shearing force and a cutting force.

The content of the fibrillated heat-resistant fiber is preferably 5 to 70% by mass, more preferably 10 to 65% by mass, more preferably 20 to 60% by mass, based on the total fiber components contained in the separator of the present invention. % by mass is more preferred. If the content of fibrillated heat-resistant fibers is less than 5% by mass, the thermal dimensional stability of the separator may deteriorate, resulting in insufficient heat resistance. On the other hand, if the content of fibrillated heat-resistant fibers exceeds 70% by mass, the mechanical strength of the separator may be insufficient.

The fibrillated cellulose used in the present invention includes regenerated cellulose fibers such as lyocell and rayon, wood fibers and wood pulp, non-wood fibers and non-wood pulp such as linters, lint, hemp and parenchyma fibers, fibrillated products, and bacterial cellulose. etc. Parenchyma fiber refers to a water-insoluble fiber containing cellulose as a main component obtained by treating, for example, with alkali the portion of parenchyma cells present in the stems, leaves, roots, fruits, etc. of plants.

The modified freeness of the fibrillated cellulose in the present invention is preferably 0 ml or more and less than 700 ml, more preferably 0 ml or more and less than 600 ml, and still more preferably 0 ml or more and less than 450 ml. If the modified freeness is 700 ml or more, the fibrillation is not so advanced and there are many thick trunk fibers, so the pore size tends to increase, and the distribution of the conductive polymer becomes uneven. Liquid retention may deteriorate. On the other hand, if the modified freeness is less than 0 ml, the average fiber length tends to be short, and the fibrillated cellulose may fall off from the separator. As the fibrillation of fibrillated cellulose progresses, the modified freeness continues to decrease. Even after the modified freeness reaches 0 ml, if the fibers are further fibrillated, the fibers will pass through the mesh and the modified freeness will start to rise. In the present invention, such a state in which the modified freeness is reversed is called "the modified freeness is less than 0 ml".

In the present invention, the fibrillated cellulose preferably has an average fiber diameter of 0.15 to 10 μm, more preferably 0.2 to 8 μm, even more preferably 0.25 to 5 μm, particularly preferably 0.25 to 5 μm. 25 to 1 μm. The average fiber diameter is the average value of the diameters of 40 fibers randomly selected from the fibers forming the separator measured by scanning electron microscope observation of the surface and cross section of the separator.

The length-weighted average fiber length of fibrillated cellulose is preferably 0.05 to 1.50 mm, more preferably 0.10 to 1.40 mm, and further preferably 0.20 to 1.30 mm. preferable. When the length-weighted average fiber length is 0.05 mm or more, it is possible to prevent an increase in the ratio of the fibers falling out of the paper mesh and being washed away into the wastewater during wet papermaking. In addition, when the length-weighted average fiber length is 1.50 mm or less, it is possible to prevent the fibers from being entangled and forming lumps, and as a result, it is possible to prevent the occurrence of thickness unevenness.

The length-weighted average fiber length of the fibrillated cellulose in the present invention is the length-weighted average fiber length (L (l) ).

The content of fibrillated cellulose in the separator of the present invention is preferably 1 to 40% by mass, more preferably 5 to 30% by mass, even more preferably 5 to 20% by mass. If the content of fibrillated cellulose is less than 1% by mass, the conductive polymer film may become non-uniform and the ESR may increase. may be higher.

The fibrillation of fibrillated cellulose in the present invention can be carried out using a refiner, a beater, a mill, a grinder, a rotary homogenizer that applies a shearing force with high-speed rotating blades, and a high-speed rotating cylindrical inner blade and fixed outer blade. A double-cylinder high-speed homogenizer that generates a shear force between them, an ultrasonic crusher that makes it finer by impact with ultrasonic waves, and a pressure difference of at least 20 MPa to the fiber suspension to pass it through a small diameter orifice to make it high speed. , It can be obtained by colliding and rapidly decelerating the fibers and treating them with a high-pressure homogenizer or the like that applies a shearing force and a cutting force to the fibers. Especially, treatment with a high-pressure homogenizer is preferable because fine fibrils can be obtained. .

The separator of the present invention contains, as a binder fiber, a core-sheath type composite fiber having a resin having a melting point of 160° C. or higher as a core component and a wet heat adhesive resin as a sheath component. Hereinafter, unless otherwise specified, "a core-sheath type composite fiber having a resin having a melting point of 160°C or higher as a core component and a wet heat adhesive resin as a sheath component" may be abbreviated as "core-sheath type composite fiber".

In the present invention, the resin having a melting point of 160° C. or higher and used as the core component of the core-sheath type composite fiber includes polyester, acrylic, polypropylene, wholly aromatic polyester, wholly aromatic polyesteramide, polyamide, semi-aromatic polyamide, and wholly aromatic resin. Polyamide, wholly aromatic polyether, wholly aromatic polycarbonate, polyimide, polyamideimide (PAI), polyetheretherketone (PEEK), polyphenylene sulfide (PPS), poly-p-phenylenebenzobisoxazole (PBO), polybenzo Resins such as imidazole (PBI) and polytetrafluoroethylene (PTFE) can be mentioned.

These core-sheath type conjugate fibers may be used alone or in combination of two or more. Among these, polyester, acryl, polypropylene, wholly aromatic polyester, wholly aromatic polyesteramide, polyamide, semi-aromatic polyamide, and wholly aromatic polyamide are preferable as the core component, and polyester, acryl, and polypropylene are more preferable.

Since the melting point of the resin used as the core component is 160° C. or higher, the shape of the core component can be maintained even during the high-temperature treatment for heat-sealing the sheath component, so excessive film formation on the surface of the separator can be suppressed. . More preferably, the melting point of the resin is 163° C. or higher. The melting point is a value measured according to JIS K7121:2012.

In the present invention, the wet heat adhesive resin used as the sheath component of the core-sheath type conjugate fiber refers to a resin that swells and gels when heated in the presence of moisture and exhibits adhesiveness, and is preferred for the separator of the present invention. In the wet papermaking method, which is a manufacturing method, the wet heat adhesive resin is swollen and gelled when the dryer is dried during wet papermaking, and the sheet is dried under heat and pressure to firmly fix other fibers. do.

Vinyl alcohol-based resins and ethylene-vinyl alcohol-based resins are preferable as the wet heat adhesive resin used in the present invention. As the sheath component of the core-sheath type composite fiber, these wet heat adhesive resins, which have excellent chemical resistance and excellent hydrophilicity, are used as the sheath component, making it possible to make a separator that is difficult to deteriorate due to electrolyte solutions. It is possible to obtain a separator having excellent water absorbability.

The volume ratio of core component/sheath component (also referred to as “core-sheath ratio”) of the core-sheath type conjugate fiber is preferably 80/20 to 40/60, more preferably 70/30 to 50/50. The core component maintains the fiber shape and mechanical strength of the fiber even after being heated. When heat is applied to the sheath component, it melts or softens to thermally bond the constituent fibers. Thermal bonding of the sheath component partially fills the voids between the constituent fibers, resulting in a more dense separator.

If the core-sheath ratio is less than 40/60 and the sheath component is too large, the constituent fibers are strongly thermally bonded, but the ratio of the core component is too small, resulting in the core-sheath type composite fiber itself becoming single. Fiber strength may decrease. Moreover, when the sheath component is large, the surface of the separator tends to form a film due to melting of the sheath component, which may deteriorate the ESR. On the other hand, if the core-sheath ratio is greater than 80/20 and the core component is too large, the single fiber strength of the core-sheath type composite fiber itself will be high, but the constituent fibers of the separator will not be sufficiently thermally bonded. Therefore, there is a possibility that the mechanical strength is lowered because the fibers are not sufficiently thermally bonded.

In the present invention, the content of the core-sheath type composite fiber is preferably 10 to 50% by mass, more preferably 15 to 45% by mass, more preferably 15 to 40% by mass, based on the total fiber components contained in the separator. % by mass is more preferred. If the content of the core-sheath type conjugate fiber is less than 10% by mass, the strength of the surface of the separator is lowered, and the fibers are likely to fall off during the capacitor element manufacturing process, possibly resulting in contamination. On the other hand, when the content of the core-sheath type composite fiber is more than 50% by mass, the surface of the separator tends to form a film, the permeability of the conductive polymer deteriorates, and the distribution of the conductive polymer becomes uneven, resulting in an ESR. may be higher.

In the present invention, the fiber diameter of the core-sheath type conjugate fiber is preferably 2 to 30 μm, more preferably 3 to 25 μm, still more preferably 4 to 20 μm. When a core-sheath type composite fiber having a fiber diameter of less than 2 μm is used, the strength of the separator may be insufficient. On the other hand, when a core-sheath type conjugate fiber with a fiber diameter exceeding 30 μm is used, the fiber dispersion during papermaking tends to be poor, and the texture of the separator tends to be uneven, which may result in an uneven conductive polymer film. be.

In the present invention, the fiber length of the core-sheath type conjugate fiber is preferably 1 to 15 mm, more preferably 2 to 12 mm, still more preferably 3 to 10 mm. If the fiber length is less than 1 mm, the strength of the separator may decrease, and if it exceeds 15 mm, the fiber dispersibility tends to decrease, the texture of the separator tends to be uneven, and the conductive polymer film may be uneven.

The separator of the present invention may contain fibers other than the fibrillated heat-resistant fiber, fibrillated cellulose and core-sheath type composite fiber described above, if necessary. For example, synthetic fibers include polyolefin, polyester, wholly aromatic polyester, polyvinyl alcohol, ethylene-vinyl alcohol copolymer, polyvinyl acetate, ethylene-vinyl acetate copolymer, aliphatic polyamide, semi-aromatic polyamide, wholly aromatic group polyamides, polyamideimides, polyimides, acrylics, polyvinyl chlorides, polyvinylidene chlorides, polyethers, polyvinyl ethers, polyvinyl ketones, polyether ether ketones, dienes, polyurethanes, polyphenylene sulfides, polybenzimidazoles, poly-p-phenylenebenzobis Examples include fibers made of synthetic resins such as oxazole, melamine, furan, urea, aniline, unsaturated polyester, fluorine, silicone, and derivatives thereof. Natural fibers include hemp pulp, cotton linter, and lint; regenerated fibers include lyocell, rayon, and cupra; semi-synthetic fibers include acetate, triacetate, and promix; inorganic fibers include alumina fiber and alumina/silica fiber. , rock wool, glass fiber, micro glass fiber, zirconia fiber, potassium titanate fiber, alumina whisker, aluminum borate whisker, and the like. The above fibers may be fibers (single fibers) made of a single resin, or composite fibers made of two or more resins. Composite fibers include core-sheath type, eccentric type, side-by-side type, sea-island type, orange type, and multi-bimetal type. Fibers having irregular cross-sections such as T-shaped, Y-shaped, and triangular cross-sections can also be included.

The thickness of the separator of the present invention is not particularly limited, but is preferably 20 μm or more, more preferably 30 μm or more, and even more preferably 40 μm or more. Moreover, it is preferably 70 μm or less, more preferably 60 μm or less, and even more preferably 50 μm or less. Even when the thickness of the separator is within the above range, the ESR of the separator of the present invention can be kept low, and the tensile strength required in the electrode lamination process can be maintained. There is no loss of workability in If the thickness of the separator exceeds 70 μm, the ESR of the separator may become too high. Also, it may not be possible to increase the capacity of the capacitor. If the thickness of the separator is less than 20 μm, the strength of the separator becomes too weak, and there is a risk of breakage during handling or cutting into narrow widths.

The density of the separator of the present invention is preferably 0.20 g/cm ³ or more and 0.50 g/cm ³ or less, more preferably 0.25 g/cm ³ or more and 0.40 g/cm ³ or less. If the density is less than 0.20 g/cm ^{3 ,} the strength of the separator becomes too weak and may be damaged during handling or cutting. In some cases, the absorbability and retention of the electrolytic solution may be lowered, and the ESR and cycle characteristics may be deteriorated.

The separator of the present invention is preferably a wet-laid nonwoven fabric produced by a wet-laid papermaking method. In the wet papermaking method, fibers are dispersed in water to form a uniform papermaking slurry, and this papermaking slurry is made by a paper machine to produce a wet nonwoven fabric. The paper machine includes a cylinder paper machine, a fourdrinier paper machine, an inclined paper machine, an inclined wire mesh paper machine, and a combination of these machines. In the process of producing the wet-laid nonwoven fabric, a hydroentangling treatment may be applied as necessary. The wet-laid nonwoven fabric may be processed by heat treatment, calendering, heat calendering, or the like.

EXAMPLES The present invention will be specifically described below with reference to Examples, but the present invention is not limited to these Examples. All parts and percentages in the examples are by mass unless otherwise specified.

<Fibrillated heat-resistant fiber>
A para-based wholly aromatic polyamide fiber was treated using a double disc refiner to obtain fibrils having a modified freeness of 350 ml, a weight-weighted average fiber length of 1.16 mm, a length-weighted average fiber length of 0.78 mm, and an average fiber width of 20 μm. A heat resistant fiber was produced.

<Fibrillated cellulose 1>
The linters are treated using a double disc refiner and further treated with a high-pressure homogenizer to obtain fibrillated cellulose 1 having a modified freeness of 0 ml, a length-weighted average fiber length of 0.22 mm, and an average fiber diameter of 0.30 μm. made.

<Fibrillated cellulose 2>
Lyocell fibers were processed using a double disc refiner to produce fibrillated cellulose 2 having a modified freeness of 90 ml, a length-weighted average fiber length of 0.86 mm, and an average fiber diameter of 0.61 μm.

<Sheath-core composite fiber 1>
A core-sheath composite fiber having a core component of polyethylene terephthalate (melting point: 255° C.) and a sheath component of ethylene-vinyl alcohol resin, with a fiber diameter of 13 μm, a fiber length of 5 mm, and a core/sheath volume ratio of 50/50. was designated as a core-sheath type composite fiber 1.

<Sheath-core composite fiber 2>
A core-sheath type composite fiber having a core component of polyethylene terephthalate (melting point: 255° C.), a sheath component of vinyl alcohol resin, a fiber diameter of 11 μm, a fiber length of 5 mm, and a core component/sheath component volume ratio of 50/50, A core-sheath type composite fiber 2 was obtained.

<Sheath-core type PET composite fiber>
The core component is polyethylene terephthalate (melting point: 255°C), and the sheath component is amorphous copolyester (melting point: 115°C) composed of a copolymer of polyethylene terephthalate and polyethylene isophthalate. Fiber diameter: 11 µm, fiber length: 5 mm. A core-sheath type polyester conjugate fiber having a volume ratio of core component/sheath component of 50/50 was used as a core-sheath type PET conjugate fiber.

<PET single fiber>
A drawn polyester fiber made of polyethylene terephthalate and having a fiber diameter of 2 μm and a fiber length of 3 mm was used as a PET single fiber.

<PP single fiber>
A drawn olefin fiber made of polypropylene and having a fiber diameter of 5 μm and a fiber length of 5 mm was used as a PP single fiber.

<Cellulose single fiber>
A rayon fiber having a fiber diameter of 9 μm and a fiber length of 3 mm was used as a cellulose single fiber.

Separators of Examples 1 to 8 and Comparative Examples 1 and 2 were produced under the following conditions.

(Manufacturing of separator)
After pouring water into a dispersion tank of 2 ^m3 , the raw materials were blended at the blending ratio (%) shown in Table 1, dispersed for 15 minutes at a dispersion concentration of 0.1% by mass, and a wet paper web was made using a cylinder paper machine. The separators of Examples 1 to 8 and Comparative Examples 1 and 2 having a width of 1000 mm were obtained by drying under hot pressure with a cylinder dryer having a surface temperature of 135°C.

The physical properties of the separators of Examples and Comparative Examples were measured and evaluated, and the results are shown in Table 2.

<Basis Weight of Separator>
The basis weight of the separator was measured according to JIS P8124:2011.

<Thickness of separator>
Using an outer micrometer specified in JIS B7502:2016, the thickness was measured under a 5N load.

<Mass retention ratio of separator after immersion in electrolyte solution>
Five test pieces with a width of 50 mm and a vertical direction of 250 mm were taken, and the mass W (g) when the water was in equilibrium was measured. It was immersed and stored in an atmosphere of 80±1° C. for 7 days. After that, the sample taken out from the γ-butyrolactone was washed with water and dried, and the sample which was brought into a water equilibrium state again was immersed in the electrolytic solution and used as a separator. The mass W ₂ (g) of the separator after being immersed in the electrolyte was measured, and the mass retention rate of the separator after being immersed in the electrolyte was obtained from the following formula and evaluated according to the following index.
Mass retention rate (%) of separator after storage of electrolyte solution = W ₂ /W x 100

A: 95% or more.
B: Less than 95%, 90% or more.
C: less than 90%.

<Strength retention rate of separator after immersion in electrolyte solution>
A separator after being immersed in the electrolyte was produced in the same manner as <Mass Retention Rate of Separator After Being Immersed in Electrolyte>. Using a desktop material testing machine (manufactured by Orientec Co., Ltd., product name STA-1150), according to JIS P8113: 2006, the test piece width is 50 mm, the grip interval is 100 mm, and the extension rate is 200 mm / min. The tensile strength in the MD direction is measured, the tensile strength before immersion in the electrolyte is T, the tensile strength after immersion in the electrolyte _{is T} , and the strength retention rate of the separator after storage in the electrolyte is obtained by the following formula. Evaluated with an index.
Separator strength retention rate (%) after electrolyte storage = T ₂ /T x 100

A: 80% or more.
B: Less than 80%, 70% or more.
C: Less than 70%.

<Friction test of separator>
A test piece cut to a width of 25 mm and a length of 250 mm is set in a Gakushin type rubbing fastness tester (manufactured by Tester Sangyo Co., Ltd., AB-301), and a 100% cotton black cloth (Billiken Moss (registered Trademark)) was used to rub the upper surface of the test piece for 6 seconds at a speed of 2 Newtons and 30 reciprocations per minute, and then the fibers adhering to the black cloth were visually determined, and the surface strength of the separator was evaluated according to the following criteria. bottom.

A: 3 or less fibers with a fiber length of 1 mm or more.
B: 4 to 10 fibers with a fiber length of 1 mm or more.
C: 11 or more fibers with a fiber length of 1 mm or more.

<Production of Solid Electrolytic Capacitor>
A separator of each example and comparative example was interposed between the anode foil and the cathode foil, which had been subjected to the etching treatment and the oxide film forming treatment, and the anode foil and the cathode foil were wound to form a capacitor element. The produced capacitor element was dried after the chemical conversion treatment. A capacitor element was impregnated with a conductive polymer aqueous dispersion of polyethylenedioxythiophene and polystyrenesulfonic acid, and then heated and dried to form a conductive polymer. Next, the capacitor element was placed in a predetermined case, the opening was sealed, and aging was performed to obtain a solid electrolytic capacitor with a rated voltage of 35 V and a rated capacitance of 100 μF.

<Production of hybrid electrolytic capacitor>
A capacitor element was produced by winding the anode foil and the cathode foil, which had been subjected to the etching treatment and the oxide film forming treatment, with the separator of each example and comparative example interposed so as not to come into contact with each other. The produced capacitor element was dried after the chemical conversion treatment. A capacitor element was impregnated with a conductive polymer aqueous dispersion of polyethylenedioxythiophene and polystyrenesulfonic acid, and then heated and dried to form a conductive polymer. Subsequently, the capacitor element was impregnated with a driving electrolyte, placed in a predetermined case, and after the opening was sealed, aging was performed to obtain a hybrid electrolytic capacitor with a rated voltage of 35 V and a rated capacitance of 150 μF.

<Measurement of ESR>
The ESR (equivalent series resistance) of the solid electrolytic capacitor and the hybrid electrolytic capacitor produced by the above method was measured with an LCR meter under the conditions of a temperature of 20°C and a frequency of 200 kHz, and the measured value of Comparative Example 1 was set to 1 and evaluated as a relative value. bottom.

As shown in Table 2, the separators produced in Examples 1 to 8 contained fibrillated heat-resistant fibers, fibrillated cellulose, and binder fibers. Since it contains a core-sheath type composite fiber with an adhesive resin as a sheath component, the mass retention rate and strength retention rate when stored in γ-butyrolactone, which is a non-aqueous solvent for the electrolyte, at high temperature (80 ± 1 ° C) It was high and excellent in electrolytic solution resistance.

From a comparison between Example 1 and Example 2, the separator of Example 1, in which the content of the core-sheath type composite fiber is 50% by mass or less with respect to the total fibers contained in the separator, contains the core-sheath type composite fiber. The ESR of the solid electrolytic capacitor and the hybrid electrolytic capacitor was lower than that of the separator of Example 2 with a ratio exceeding 50% by mass, and favorable results were obtained.

From a comparison between Example 3 and Example 4, the separator of Example 3, in which the content of the core-sheath type conjugate fiber is 10% by mass or more with respect to the total fibers contained in the separator, contains the core-sheath type conjugate fiber. As a result of the friction test, the surface strength of the separator was superior to that of the separator of Example 4 having a ratio of less than 10% by mass.

From the comparison between Example 7 and Example 8, the separator of Example 8, in which the binder fiber is a core-sheath type composite fiber whose sheath component is ethylene-vinyl alcohol resin, has a core whose sheath component is vinyl alcohol resin. The ESR of the solid electrolytic capacitor and the hybrid electrolytic capacitor was lower than that of the separator of Example 7 in which the sheath-type composite fiber was used as a binder, and favorable results were obtained.

The separators of Comparative Examples 1 and 2, in which the core-sheath type PET composite fiber was used as the binder fiber, had a low mass retention rate of the separator after immersion in the electrolyte and a low strength retention rate of the separator after immersion in the electrolyte, and were inferior in electrolyte resistance. result.

The separator for solid electrolytic capacitors or hybrid electrolytic capacitors of the present invention can be suitably used for solid electrolytic capacitors and hybrid electrolytic capacitors.

Claims (3)

It contains a fibrillated heat-resistant fiber, a fibrillated cellulose and a binder fiber, and the binder fiber includes a core-sheath type composite fiber having a resin having a melting point of 160°C or higher as a core component and a wet heat adhesive resin as a sheath component. A separator for a solid electrolytic capacitor or a hybrid electrolytic capacitor, wherein the wet heat adhesive resin is at least one selected from the group consisting of vinyl alcohol resins and ethylene-vinyl alcohol resins. 2. The separator for a solid electrolytic capacitor or hybrid electrolytic capacitor according to claim 1 , wherein the content of the core-sheath type composite fiber is 10 to 50% by mass with respect to the total fibers contained in the separator. 3. A solid electrolytic capacitor or hybrid electrolytic capacitor using the separator for a solid electrolytic capacitor or hybrid electrolytic capacitor according to claim 1 or 2 .